1 research outputs found
Bulk Immiscibility at the Edge of the Nanoscale
In the quest to identify more effective
catalyst nanoparticles
for many industrially important applications, the Au–Pt system
has gathered considerable attention. Despite considerable effort the
interplay between phase equilibrium behavior and surface segregation
in Au–Pt nanoparticles is still poorly understood. Here we
investigate the phase equilibrium behavior of 20 nm Au–Pt nanoparticles
using a combination of high-resolution scanning transmission electron
microscopy and a hybrid Monte Carlo and molecular dynamics atomistic
simulation technique. Our approach takes into account the effects
of immiscibility, elastic strain, interfacial free energy, and surface
segregation. This is used to explain two key phenomena taking place
in these nanoparticles. The first is whether the binary system remains
immiscible at the nanoscale, and if so what morphology would the secondary
phase take. Our findings suggest that even at sizes of 20 nm, thermally
equilibrated Au–Pt nanoparticles remain largely immiscible
and behave thermodynamically as bulk-like systems. We explain why
20 nm Au–Pt nanoparticles phase separate into hemispheres as
opposed to a thick-shelled core–shell structure. These insights
are central to further optimization of Au–Pt nanoparticles
toward enhanced catalytic activities. The phase-separated Janus particles
observed in this study offer enhanced material functionality arising
from the nonuniformity of their plasmonic, catalytic, and surface
properties